The proposed research derives from three themes: 1) physical factors and non-neural structures in the nasal cavities govern much of th functioning of olfaction and the common-chemical sense, 2) joint assessment of olfaction and the common-chemical sense can highlight their similarities and differences more keenly than independent study of each modality, and 3) influence of combinations of stimuli will reveal much about the physical and chemical properties of importance to the chemosensitive modalities. Four topics will receive attention: 1) the influence of temperature and humidity on perceived odor and irritation, 2) the relation between differential sensitivity and growth of perceived odor magnitude with concentration, 3) a search for commonality among odorous stimuli by means of a procedure that combines the influence of cross-adaptation, masking, and the additivity of mixtures, and 4) the functional organization of the central neural locus of olfactory adaptation. Psychophysical procedures will range from those of signal detection theory to ratio-scaling techniques. The investigation of temperature and humidity will employ an all-weather chamber and will compare transient changes in environmental condition to steady state conditions. The outcome may help to guide choice of ventilation rates for occupied spaces. The investigation of differential sensitivity will assess the limiting influence of noise in the stimulus and will seek to relate the index of sensitivity to such physical measures as the retention time of odorants in the nasal cavity. The investigation commonality will include the evaluation of odor counteractants. Experiments on the central locus of adaptation will explore the ability of an adapting stimulus inhaled via one nostril to diminish the perceived magnitude of stimuli inhaled via the contralateral nostril. Both self-adaptation and cross-adaptation will receive attention. Choice of stimuli has been guided in part by the outcome of various physiolocial, biophysical, or biochemical investigations. Some experiments will also explore malodors.